In a known injection molding process, a transfer film, e.g., a decorative film or a functional film is transferred to a molded article during injection molding. The injection molding process typically has the following steps:
First, a film including a base film and a transfer film, e.g., a decorative film or a functional film stacked on the base film is fed between a first die and a second die, which are shaping dies constituting a mold, from the upstream side of the dies. At this point, tension is applied to the film having a flat surface. The surface of the film interposed between the first die and the second die is disposed in parallel with a mold parting face that is the parting face of the first die.
Subsequently, the film is fixed to the parting face of the first die with a clamping tool. After that, the film is sucked to a molding surface that is the inner surface of the recessed portion of the first die. This stretches the film along the molding surface of the first die as much as possible.
Subsequently, the second die is moved to the first die so as to close the mold composed of the first die and the second die. At this point, the first and second dies and the clamping tool come into contact with each other, forming a cavity having a predetermined shape.
After that, a predetermined amount of molten resin is injected into the cavity having the predetermined shape in the closed mold. The injected molten resin is then cooled. This solidifies the resin into a molded article having the predetermined shape. Through this process, the transfer film stacked on the base film is transferred to the surface of the molded article.
After a certain cooling period, the second die is separated from the first die so as to open the mold composed of the first and second dies. The molded article is then removed from the opened mold. After the removal of the molded article, the clamping tool is separated from the parting face of the first die and then the film is transported downstream of the mold, separating the base film from the recessed portion of the first die.
The film is rolled on a shaft in a film feeder disposed upstream of the mold. The film drawn from the film feeder is looped over a shaft in a film winder disposed downstream of the mold. When the rolled film fed from the film feeder is wound by the film winder, the shaft in the film feeder and the shaft in the film winder are rotated by different motors so as to apply predetermined tension to the film.
As has been discussed, the film including the transfer film, e.g., a decorative film or a functional film stacked on the base film is inserted between the first and second dies that are shaping dies for injection molding of resin materials, and then the shaping dies are closed. Subsequently, molten resin is injected onto the film contained in the shaping dies so as to transfer the transfer film, e.g., a decorative film or a functional film onto a molded article while molding the injection molded article with high accuracy.
For example, Japanese Patent Laid-Open No. 7-60791 describes an example of the injection molding process. Japanese Patent Laid-Open No. 7-60791 describes an injection molding method and an injection molding machine which transfer a decorative film, that is, a pattern to the surface of a molded article while injection-molding the molded article by means of a film including the decorative film stacked with the printed pattern on a base film. FIG. 8 is a cross-sectional view of the injection molding machine described in Japanese Patent Laid-Open No. 7-60791.
In the injection molding machine of FIG. 8, first, a film 100 including a decorative film stacked with a printed pattern on a base film is caused to travel between a first die 201 and a second die 202, and then the pattern is positioned between the first die 201 and the second die 202.
Subsequently, in the injection molding machine of FIG. 8, the film 100 is fixed on the parting face of the first die 201 with a clamping tool 203 and then is sucked on a molding surface that is the inner surface of the recessed portion of the first die 201. This stretches the film 100 along the molding surface of the first die 201 as much as possible.
After that, in the injection molding machine of FIG. 8, a mold composed of the first die 201 and the second die 202 is closed, and then molten resin is injected into a cavity 204 formed in the closed mold. The injected molten resin is then cooled in the injection molding machine of FIG. 8. Thus, the resin is solidified into a molded article 300. Furthermore, a pattern is transferred to the surface of the molded article 300 through this process.
Subsequently, in the injection molding machine of FIG. 8, the mold composed of the first die 201 and the second die 202 is opened and then the molded article 300 is removed from the opened mold. After that, in the injection molding machine of FIG. 8, the clamping tool 203 is separated from the parting face of the first die 201 and then the film 100 is wound on a shaft in a film winder (not shown). This separates the base film from the recessed portion of the first die 201 and feeds the film 100 downstream of the mold.
Also in the injection molding machine of FIG. 8, tension is applied to the film 100 traveling between the first die 201 and the second die 202, flattening the surface of the film 100 in parallel with a mold parting surface that is the parting surface of the first die 201.
As has been discussed, typically, the film is fixed to the parting surface of the first die with the clamping tool and then is drawn into the recessed portion of the first die by suction before molten resin is injected. Thus, the film is partially stretched.